The History of Life on Earth

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The History of Life on Earth

• Chapter 22

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The Fossil Record
reveals broad patterns in the evolution of life.
Fossils show that many evolutionary changes are
gradual.
Incomplete but getting better...
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The Fossil Record
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The Fossil Record
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The Fossil Record
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Origins of life on Earth

• Prebiotic evolution
• Evolution before life existed abiotic synthesis
  of organic molecules
• The primordial environment
• Hot
• Early atmosphere carbon dioxide, methane,
  ammonia, hydrogen, nitrogen, hydrochloric acid,
  hydrogen sulfide, and water vapor
• The possible origin of organic molecules
• 1953the Stanley Miller experiment
• Reproduced atmosphere of early times
• Simple organic molecules appeared after a few
  days
• Origins of life on Earth

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The first cells

• Age of microbes3.5 billion years ago
• Precambrian era
• The earliest living cellsanaerobic prokaryotes
• Photosynthetic bacteria
• Used suns energy
• Need hydrogen (hydrogen sulfide then used water)
• Oxygen-rich environment (2.2 bya)
• Water-based photosynthesis releases oxygen as
  by-product
• Development of aerobic metabolism

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Fish

• 500 mya fish developed
• Internal skeleton for support
• By 400 mya fish were a prominent group
• Became dominant predator of the open seas

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The transition to land

• Advantages of terrestrial living (plants)
• Better opportunities for sunlight
• Soils rich in nutrients
• At the beginning, no predators
• Challenges of terrestrial living (plants and
  animals)
• Gravity
• Finding water
• Gametes need to be protected from drying out

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The transition to land (cont.)

• The evolution of land plants (400 mya)
• In the beginning, low growing plants
• Conserve water waterproof coatings, root-like
  structures
• Staying upright extra thick cell walls to be
  able to stand upright
• The first land plants
• Mosses and ferns
• Continued water dependency (swamps and marshes)
• Seed bearing plants (375 mya)
• the invasion of dry habitats
• New kind of seed bearing plant (286-245mya)
• Conifers cone bearing

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The transition to land (cont.)

• Flowering plants (140 mya)
• The dominant plant form today
• Pollination by insects and other animals

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The evolution of terrestrial animals

• Arthropods
• Todays group includes insects, spiders, crabs,
  scorpions, and centipedes
• By chance, suited to land
• Exoskeleton
• Waterproof and strong for support against force
  of gravity
• Lobefin fish to amphibians
• 2 features that would eventually enable
  descendents to go to land
• Stout, fleshy fins that were used to crawl on the
  bottom
• Outpouching of the digestive tract that could
  fill with air (like a primitive lung)
• Improvement of legs and lungs amphibians
  evolved
• 350 mya
• Respire using gills as larvae and lungs as adults
• Still needed to remain near water
• Frogs, toads, salamanders
• Amphibians to reptiles
• Climate turning drier, group of amphibians
  developing adaptations
• Reptiles (snakes, turtles, lizards, crocodiles)
• Four major adaptations to land
• Internal fertilization

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The age of the dinosaurs

• Flourished for over 100 million years
• Extinct about 65 million years ago
• Some reptiles remained small
• Had to maintain body temperature so only active
  when the air was warm
• Two groups of small reptiles independently
  evolved they developed insulation
• Evolved feathers
• Evolved hair

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The evolution of terrestrial animals

• Birds
• Insulating feathers retain body heat
• Evolution of feathers for flight
• Mammals
• Insulating hair retains body heat
• Hair found in coprolites (fossilized animal
  feces)
• Presumed to have hair at least 55 mya
• Live births and mammary glands
• Not able to find reproductive organs in fossil
  record

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Mass Extinctions
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Mass Extinctions

• Contributing Factors
• Climate change
• Plate tectonics
• Huge plates of the earths crust move about the
  planets surface resulted in continental drift
• Catastrophic events
• Meteorites
• Proposed dinosaur extinction 65mya

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Continental Drift from Plate Tectonics
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Human evolution

• Primate evolution (lemurs, monkeys, apes, and
  humans)
• Grasping handsprecision grip and power grip
• Binocular and color vision with overlapping
  fields of view
• Large brainallows fairly complex social systems

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Human evolution

• The evolution of dryopithecinesbetween 20 and
  30 million years ago
• Diverged from tree-dwelling monkey line and
  became land dwellers
• Ancestral to the hominid

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Human evolution

• Hominid evolution
• Diverged from ape lineage 5-8mya
• Ardipithecus near split from apes on family
  tree (4.4mya)
• Australopithecinesthe first true hominids
• Appeared 4mya as evidenced by fossils
• Walked upright
• Large brains

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Human evolution

• Hominid evolution (cont.)
• Homo habilis2.5 million years ago
• Homo ergaster 2 million years ago
• Larger body and brain
• Ability to make crude stone tools
• Ancestor to 2 distinct branches of hominids
• Homo erectus
• Neanderthals and Homo sapiens

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Hypothetical Family Tree for Humans
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Human evolution

• Homo erectus1.8 million years ago
• Face of modern human
• More socially advanced
• Sophisticated stone tools aided in hunting
• Used fire

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Human evolution

• Neanderthals evolved 150,000 years ago
• Similar to humansmuscular, fully erect,
  dexterous, large brains
• Developed ritualistic burial ceremonies
• Once believed to be a variety of Homo sapiens,
  but DNA evidence has shown that they did not lead
  to modern humans
• Spread throughout Europe and western Asia, but
  went extinct 30,000 years ago

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Representative Hominid Tools
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Human evolution

• Homo sapiens150,000 years ago
• Cro-Magnons evolved 90,000 years ago
• Named after the region where the remains were
  found
• European and Middle Eastern fossils
• Direct descendants of modern humans
• Domed heads, smooth brows and prominent chins
• Were artistic and made precision tools